A plurality of service systems for providing services to users are present on the Cloud platform such as IaaS (Infrastructure as a Service). Such service systems have various types such as EC (Electronic Commerce) system and animation distribution system. An individual service system includes a plurality of nodes such as Web server, application server and database server. Application server may be denoted as App server in the following. Database server may be denoted as DB server.
PTL 1 describes therein a virtual resource operation and management system. The operation and management system described in PTL 1 is to control a virtual system whose structure is defined in a template.
A virtual server resource adjustment system described in PTL 2 calculates the amount of empty resource as the amount of resource capable of being reduced based on the amount of currently-allocated resource and sums up the respective amounts of empty resources thereby to calculate the total amount of empty resources for the respective virtual servers. The virtual server resource adjustment system then calculates the amount of resource to be added based on a high load of a virtual server, and compares it with the total amount of empty resources. When the total amount of empty resources is larger, the virtual server resource adjustment system determines that the resource can be added. PTL 2 lists, as exemplary resources, CPU (Central Processing Unit), memory, disk I/O (Input/Output), and network I/O.
PTL 3 discloses therein a structure in which a client and servers are provided and data resources are divided into some servers. PTL 3 describes that loads on the servers are to be balanced.